1. Field of the Invention
The present invention relates generally to semiconductor wafer cleaning. More specifically, the present invention relates to an apparatus for clamping a wafer in a wafer processing chamber and a method for operating the wafer clamping apparatus.
2. Description of the Related Art
In the manufacture of semiconductor devices, a surface of a semiconductor wafer (“wafer” or “substrate”) must be cleaned to remove chemical and particulate contamination. If the contamination is not removed, semiconductor devices on the wafer may perform poorly or become defective. Particulate contamination generally consists of tiny bits of distinctly defined material having an affinity to adhere to the surface of the wafer. Examples of particulate contamination can include organic and inorganic residues, such as silicon dust, silica, slurry residue, polymeric residue, metal flakes, atmospheric dust, plastic particles, and silicate particles, among others.
Some types of wafer cleaning processes are performed in a sealed chamber. An important aspect of the chamber design is the method by which the wafer is held or clamped within the chamber. The wafer should be held securely within the chamber to prevent lifting or mobilization of the wafer. With lifting or mobilization, the wafer is exposed to a significant risk of damage. Also, lifting of the wafer will cause the backside of the wafer to be more exposed to cleaning fluids and by-products within the chamber. Exposure of the backside of the wafer to cleaning fluids and by-products can result in increased contamination and cleaning difficulty. Thus, it is important to securely hold the wafer within the chamber during processing.
One conventional option for securing the wafer within the chamber includes clamping the wafer through contact with the wafer top surface. Using clamps in contact with the wafer top surface introduces a potential for causing damage at the clamp-to-wafer interface. Another conventional option for securing the wafer within the chamber includes using an electrostatic chuck to pull the wafer down to a support. Use of an electrostatic chuck can increase the complexity of the chamber design. For example, if the chamber is designed with a pressure boundary, the equipment associated with the electrostatic chuck (e.g., power supply) must be compatible with maintaining the integrity of the pressure boundary. The conventional options for securing the wafer in the chamber can be problematic with respect to wafer damage and implementation complexity, particularly when the chamber incorporates a pressure boundary. To ensure the integrity of the wafer and to simplify the chamber design, it is preferable to secure the wafer within the chamber without the use of clamps contacting the wafer top surface and without the use of an electrostatic chuck.
In view of the foregoing, there is a need for a wafer clamping apparatus that will effectively secure the wafer within the chamber during wafer processing. The wafer clamping apparatus should be implemented without contacting the wafer top surface and with minimal increase in chamber design complexity.